State of the art in wireless sensing with surface acoustic waves

Surface acoustic wave (SAW) devices can be turned into novel identification and sensor elements (transponders) that do not need any power supply and may be interrogated wirelessly. Such a transponder picks up an electromagnetic request signal and stores it until all echoes caused by multipath propagation have died away. Then, a characteristic response signal is beamed back to the interrogator unit. In radio-link sensors, a physical or chemical quantity influences the propagation properties of the SAW and consequently changes the response pattern of the device. This contribution surveys the operating principle of such sensors and their state-of-the-art performance. The discussion is supported by illustrative examples such as temperature sensors and sensors for mechatronic applications.